Carbon nanotubes (CNT) are promising materials for transparent conduction as a result of their exceptional electrical, optical, mechanical, and chemical properties. Ultra thin films based on CNT networks above the percolation limit have beneficial attributes such as stiffness and chemical stability that makes it superior to indium tin oxide (ITO) in certain applications. CNT nano-mesh films exhibit flexibility, allowing films to be deposited on pliable substrates prone to acute angles, bending, and deformation, without fracturing the coating. Modeling work has shown that CNT films may offer potential advantages such as, for example, tunable electronic properties through chemical treatment and enhanced carrier injection owing to the large surface area and field-enhanced effect at the nanotube tips and surfaces. It is also recognized that although ITO is an n-type conductor, such CNT films can be doped p-type and, as such, can have applications in, for instance, the anode or injecting hole into OLED devices, provided the films are smooth to within 1.5 nm RMS roughness.
Although ITO films still lead CNT films in terms of sheet conductance and transparency, the above-mentioned advantages together with potential cost reductions have stimulated significant interest in exploiting carbon nanotube films as transparent conductive alternative to ITO. In order to live up to its expectations, CNT films should display high transparency coupled with low sheet resistance. The relationship between transparency and sheet resistance for thin conducting films is controlled by the ratio of dc conductivity and optical conductivity, σdc/σopt, such that high values of this ratio typically are most desirable.
However, to date, viable CNT synthetic methods yield poly-dispersed mixtures of tubes of various chiralities, of which roughly one-third are metallic with the remainder being semiconducting. The low σdc/σopt performance metric of such films is largely related to the large fraction of semiconducting species. These semiconducting tubes, in turn, also give rise to the bundling of the tubes, which tends to increase the junction resistance of the film network.
The typical value of σopt for CNT films depends on the density of the film. Just above the percolation limit, this value tends to close at 1.7×104 μm at 550 nm, while the de electrical conductivity to date is in the region of 5×105 S/m. However, industry specifications require better than 90% transmission and less than 90 ohms/square sheet resistance. To achieve these values, one can determine that the necessary dc conductivity be in excess of 7×105 S/m. Thus, it will be appreciated that there is a need in the art for improving the electronic quality of even the best CNT films so that the σDC/σopt ratio, in turn, is improved. This poly-dispersity stems from the unique structure of SWNTs, which also renders their properties highly sensitive to the nanotube diameter.
Certain example embodiments of this invention relate to the deposition of nano-mesh CNT films on glass substrates and, in particular, the development of coatings with high σdc/σopt on thin, low iron or iron free soda lime glass and/or other substrates (e.g., other glass substrates such as other soda lime glass and borosilicate glass, plastics, polymers, silicon wafers, etc.). In addition, certain example embodiments of this invention relate to (1) finding viable avenues of how to improve the σdc/σopt metric via stable chemical doping and/or alloying of CNT based films, and (2) developing a large area coating technique suitable for glass, as most work date has focused on flexible plastic substrates. Certain example embodiments also pertain to a model that relates the morphological properties of the film to the σdc/σopt.
In certain example embodiments of this invention, a solar cell is provided. A glass substrate is provided. A first CNT-based conductive layer is located, directly or indirectly, on the glass substrate. A first semiconductor layer is in contact with the first CNT-based conductive layer. At least one absorbing layer is located, directly or indirectly, on the first semiconductor layer. A second semiconductor layer is located, directly or indirectly, on the at least one absorbing layer. A second CNT-based conductive layer in contact with the second semiconductor layer. A back contact is located, directly or indirectly, on the second CNT-based conductive layer.
In certain example embodiments of this invention, a photovoltaic device is provided. A substrate is provided. At least one photovoltaic thin-film layer is provided. First and second electrodes are provided. First and second transparent, conductive CNT-based layers are provided. The first and second CNT-based layers are respectively doped with n- and p-type dopants.
In certain example embodiments of this invention, a touch panel subassembly is provided. A glass substrate is provided. A first transparent, conductive CNT-based layer is provided, directly or indirectly, on the glass substrate. A deformable foil is provided, with the deformable foil being substantially parallel and in spaced apart relation to the glass substrate. A second transparent, conductive CNT-based layer is provided, directly or indirectly, on the deformable foil. A touch panel assembly including a display (which itself may include one or more CNT-based layers) also may be provided in certain example embodiments of this invention.
In certain example embodiments of this invention, a data/bus line comprising a CNT-based layer supported by a substrate is provided. A portion of the CNT-based layer has been exposed to an ion beam/plasma treatment and/or etched with H*, thereby reducing conductivity of the portion.
In certain example embodiments, a method of making an electronic device is provided. A substrate is provided. A CNT-based layer is provided on the substrate. The CNT-based layer is doped. The CNT-based layer is selectively patterned by one of: ion beam/plasma exposure and etching with H*.
In certain example embodiments, a method of making an article for a refrigeration or freezer unit is provided. First and second substantially parallel and spaced apart glass substrates are provided, with the first substrate being provided for an interior side of the article and the second substrate being provided for an exterior side of the article. One or more transparent conductive coatings (TCCs) are disposed, respectively, on one or more major surfaces of the first and/or second substrates. At least the first and second substrates are thermally tempered (e.g., with the one or more TCCs thereon). Each said TCC includes at least one CNT-inclusive layer.
In certain example embodiments, a rain sensor is provided. A sensing circuit comprises at least first and second sensing capacitors that are sensitive to moisture on an external surface of a window, with each said sensing capacitor including at least one CNT-based layer. The sensing circuit further comprises at least one mimicking capacitor that mimics at least one of charging and discharging of at least one of the first and second sensing capacitors. A writing pulse causes at least the first sensing capacitor to be charged, and an erasing pulse causes each of the first sensing capacitor and the mimicking capacitor to substantially discharge. Presence of rain on the external surface of the window in a sensing field of the first sensing capacitor causes a voltage at an output electrode of the mimicking capacitor to fluctuate in a manner proportional to fluctuation of voltage at an output electrode of the first sensing capacitor, even though the rain is not present in a field of the mimicking capacitor. Rain is detected based on an output signal from the output electrode of the mimicking capacitor. The output signal is read at least between an end of the writing pulse and a beginning of the erase pulse. The mimicking capacitor is physically separated from the sensing capacitors. The writing pulse causes the first sensing capacitor, but not the second sensing capacitor, to charge and also causes the mimicking capacitor to charge.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.